In response to PAR-03-137, we are submitting a program proposal to design and develop a series of potent and highly selective protein-based topical microbicides. The unifying theme of the application is the use of non-pathogenic mucosal bacteria, lactobacilli, to deliver these proteins to mucosal surfaces within the vagina and rectum. The administration of genetically modified vaginal isolates of lactobacilli, expressing protein microbicides, is anticipated to prevent access or entry of HIV into host cells and tissues, thereby reducing infection. The three highly integrated projects include 1) an approach to design and develop lactobacilli expressing CD4 variants capable of a multivalent high-avidity interaction with HIV, as a means of trapping and inactivating HIV particles within the mucosa, 2) a program to produce lactobacilli expressing RANTES analogs that function as chemokine receptor antagonists and block HIV entry into cells and tissues of the host and 3) a project centered on lactobacillus-directed delivery of anti-ICAM derivatives as a novel means of inhibiting cell-associated mucosal transmission of HIV. These projects all will be supported by central core facilities, including administrative, microbiology, and primate safety study cores. Importantly, the three unique projects highlighted in this application have already completed key "proof-of-concept" studies that set the stage for the advanced research and development activities outlined in this application. Furthermore, all three approaches target conserved functional mechanisms used by HIV to achieve a productive infection of its host. As such, these approaches are less likely to be circumvented by the high mutability of viral proteins, an important property of HIV that has impaired the development of effective preventative vaccines.